(1) Field of the Invention
The present invention relates to an improved cable section assembly including a core structure and a protective outer casing for marine applications and a method for forming said cable assembly. The invention is of utility in connection with such assemblies employ by the U.S. Navy as buoyant antenna sections. An example of a cable section and antenna component is disclosed in U.S. Pat. No. 6,426,464, issued 30 Jul. 2002, which is hereby incorporated by reference in its entirety. An example of a composition of material for the core structure which provides buoyancy is disclosed in U.S. Pat. No. 5,606,329 issued 29 Feb. 1997, also hereby incorporated by reference in its entirety.
(2) Description of the Prior Art
Cables have been used for a wide variety of marine purposes. U.S. Pat. No. 3,434,104 to Stapleton et al., for example, illustrates a hydrophone cable constructed of a plurality of sections which are so constructed and arranged as to provide protection to the sensing devices carried thereby. The cable includes a body of cellular material, such as foamed polyurethane, provided with cavities in its exterior surface, in which crystal detectors are recessed. The cable further includes a waterproof jacket enclosing the cellular material body. A floatation liquid is contained in a space between the outer jacket and the body. Further, strain members and electrical conducting wires are enclosed within the body.
U.S. Pat. No. 3,480,907 to King illustrates a neutrally buoyant hydrophone streamer in which solid polymeric material, having a plurality of discrete air-filled particles distributed throughout, fills all remaining space within a hollow jacket.
U.S. Pat. No. 3,744,016 to Davis describes a buoyant seismic streamer housing cable and its electronics. A syntactic foam is molded about the cable/electronics. An abrasion resistant sheathing encases the syntactic foam.
U.S. Pat. No. 3,900,543 to Davis describes yet another neutrally buoyant seismic hydrophone streamer. The streamer is constructed by extruding a syntactic foam material comprising an elastomeric material and gas filled microspheres onto a central stress member to form an elongated streamer member. The streamer is then covered with a water and oil resistant, abrasion resistant covering. It may be provided with exteriorly affixed hydrophones or hydrophones that can be affixed to the foam core. An outer protective sheath can be extruded or otherwise provided around the streamer and the hydrophones. Extrusion is effected utilizing a suitable elastoplastic material which can be extruded at pressures below about 300 psi.
U.S. Pat. No. 4,733,379 to Lapetina et al. illustrates a flexible line array assembly which includes an array of spaced-apart piezoelectric elements arranged in a line. Electrodes are disposed on the opposing surface areas of the elements and are coupled to conductors which carry signals produced by the piezoelectric elements when the elements are stressed by acoustical signals. A porous, open-cell material is disposed about the piezoelectric elements as an encasement to maintain the elements in place and mechanically isolate the elements. An outer, water-tight jacket encloses the open cell material and holds a fill fluid carried within the open-cell material. An electrically conductive flexible sleeve is placed either about the open-cell material or about the outer jacket to shield the piezoelectric elements from electromagnetic waves.
U.S. Pat. No. 4,963,420 to Jarrin et al. describes a buoyant cable assembly which uses a polyethylene material to separate tubes or cables and a thermoplastic material as an external sheath. An extrusion process is used to form the cable.
In the late 1980s, a new capability was conceived for a buoyant cable antenna (BCA) which would extend its frequency range. A requirement of this new system was that the electronic circuit boards be distributed throughout a section of the BCA. Thus, the previously used amplifier chassis could no longer be used.
Current BCAs are made of polyethylene. Because polyethylene requires high heat in the molding process, it has been dismissed as a molding material for fear that the electronics would be damaged by the extreme heat. Thus, a room temperature curing compound, polyurethane, has been selected as the molding compound.
The potted circuit boards used in the BCAs have to withstand the flexing that the BCA assembly undergoes while deployed at sea. To accomplish this, the circuit boards are potted in a polyurethane that exhibits a high durometer reading. The areas between the molded circuit boards are then overmolded with a microballoon filled polyurethane compound to provide buoyancy.
After fabricating and testing a few of these BCA assemblies, it became apparent that the buoyant polyurethane compound was not durable enough to withstand the deployment process. The compound could be over-flexed during handling, causing cracks and breaks to occur. When deployed using a standard Navy capstan, the assembly was easily gouged and its integrity was frequently compromised. After only a few deployments, the test assemblies quickly deteriorated to the point where they were torn apart by the capstan mechanism. In addition, the possibility that the polyurethane compound would become saturated with water during testing at pressure and thereby exhibit different mechanical properties and possibly a decrease in buoyancy, was also of serious concern.
Thus, there remained a need for a rugged cable assembly which can withstand the rigors of deployment and handling.